The present invention relates to anti-siphon valves (or non-return valves) for medical infusion lines and the like.
The said valves traditionally comprise a first tubular element and a second tubular element which respectively define a passage upstream and a passage downstream, which are coaxial with one another, and between which is transversely set a diaphragm made of elastically deformable material which cooperates, in a fluid-tight manner, with an annular valve seat of said first tubular element to keep the anti-siphon valve normally closed, and in which a predetermined fluid pressure in said passage upstream causes a deflection of the diaphragm and the consequent opening of the anti-siphon valve.
These valves, which are normally closed, must be able to open promptly when the pressure in the passage upstream is higher than a pre-set threshold value, which is much higher than the one in normal anti-siphon valves used in similar medical applications, and is typically between 1 and 5 psi.
The primary purpose of the present invention is to provide a valve of the type specified above, which is shaped in such a way as to be able to withstand a relatively high closing preloading, at the same time developing a considerable opening force whenever the fluid pressure in the passage upstream exceeds, albeit by a small amount, the threshold value for which the valve is calibrated.
Another purpose of the present invention is to provide a valve of the aforesaid type, which is shaped so as to meet the above requirement with a simple and inexpensive structure, also in terms of assembly.
A further purpose of the invention is to provide a valve of the aforesaid type that is easy to calibrate, at the moment of fabrication, according to the requirements of use.
According to the invention, the above purpose is achieved essentially thanks to the fact that the said annular valve seat is defined by a conical-surface wall of said first tubular element which diverges towards said second tubular element, and the aforesaid diaphragm consists of the bottom wall of a cup-like element the external peripheral edge of which is normally kept pressed in fluid-tight contact against the annular valve seat under the axial thrust exerted by the side wall of said cup element; the deflection of said bottom wall of the cup element brought about in use by said pre-determined fluid pressure determining the radial contraction of said external peripheral edge and its consequent separation from said annular valve seat.
Thanks to this solution idea, during use, opening of the valve takes place promptly even if the diaphragm consisting of the bottom wall of the cup-like element is subjected to a high axial preloading which ensures maximum safety and reliability of closing of the valve. In fact, the thrust exerted by the pressure upon reaching of the threshold value against the bottom wall of the cup-like element produces an elastic deformation of the latter into a concave conformation which is substantially hemispherical, and as a result of which the peripheral edge of said bottom wall separates from the conical-surface valve seat with an effect which is, so to speak, amplified. In practice, a modest pressure value beyond the above-mentioned threshold value is therefore sufficient to cause opening of the valve according to the invention in a prompt and immediate way.
In the valve-open condition, as the flow rate of the fluid increases there is a proportionally greater deformation of the bottom wall of the cup-like element and, consequently, a proportionally greater removal of its peripheral edge from the valve seat. In this way, the head loss through the valve follows a linear pattern.
In addition, in the valve-open condition, the thrust exerted by the fluid against the external surface of the area of the side wall of the cup element which is adjacent to the bottom wall contributes to keeping the valve open.
According to a preferred embodiment of the invention, the free edge of the side wall of said cup element conveniently rests against a grooved surface of said second tubular element communicating with said passage downstream, and the side wall of the cup element conveniently has a conical surface diverging towards said grooved surface of the second tubular element.
Alternatively, said surface may be cylindrical.